1. Field of the Invention
The present invention relates to solid organic phosphites resistant to hydrolysis, and to the process for preparing them.
Organic phosphites are compounds which are used in the art in order to endow organic polymers with stability characteristics, against the oxidative degradation caused by light and/or heat, such as disclosed, e.g., in U.K. Patent No. 803,557 and U.S. Pat. No. 3,516,963.
The organic phosphites suffer from the undesired characteristic of undergoing phenomena of hydrolysis, in particular during their storage under warm and moist conditions, with the consequent loss of stabilizing activity, and danger of possible handling problems.
It is known to coat solid phosphite powders with dialkoxy or diphenoxy substituted silicones such as those of the formula: ##STR1## wherein R.sup.5 is an alkoxy or phenoxy group and m is greater than 4. Such disubstituted silicones can however undergo a reaction with water, thereby generating an alcohol or phenol which can in turn react with the phosphite. Thus while coatings of disubstituted silicones can provide solid phosphites with some degree of protection from hydrolysis, they themselves can result in degradation through their secondary hydrolysis byproducts. Other processes for coating phosphites include treating said powdered phosphites with a monomeric silane containing in its molecule at least two alkoxy groups and causing the silane to hydrolyze, thereby causing the formation of a siliconic polymer on the surface of powder particles but again generating alcohol upon hydrolysis that can react with the phosphite. Neri et al. U.S. Pat. No. 4,810,579 issued Mar. 7, 1989 discloses organic phosphite in powder form treated with a silane containing in its molecule at least two alkoxy groups, and is incorporated herein by reference.
Consequently, there is a desire to improve the hydrolytic stability of silicone coated solid organic phosphites.